Tropical Depression EIGHT (Text)

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TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082007
1100 PM EDT WED SEP 12 2007
THE DEPRESSION HAS NOT APPRECIABLY CHANGED IN ITS CONVECTIVE
ORGANIZATION OR ESTIMATED INTENSITY SINCE THIS AFTERNOON. WHILE
DVORAK...ADT...AND AMSU ESTIMATES ARE AT MINIMAL TROPICAL STORM
INTENSITY...SSMI AND SSMIS MICROWAVE IMAGERY SUGGESTS INSTEAD THAT
THE CENTER OF THE SYSTEM IS OFFSET ON THE NORTHEAST SIDE OF THE
CONVECTION. UPPER TROPOSPHERIC MOTION VECTORS SHOW THAT THERE
REMAINS SOME MODERATE NORTHEASTERLY SHEAR THAT CONTINUES TO IMPACT
THE SYSTEM. SINCE THE ESTIMATED CENTER IS NOT WELL EMBEDDED WITHIN
THE CONVECTION...THIS INDICATES THAT THE SYSTEM REMAINS A TROPICAL
DEPRESSION AT THIS TIME.
TD EIGHT IS SOUTH OF A WEAK DEEP LAYERED RIDGE WHICH IS CURRENTLY
PROVIDING A STEERING OF ABOUT 280/10...SLIGHTLY MORE WESTWARD THAN
INDICATED IN THE PREVIOUS ADVISORY. ALL OF THE GLOBAL AND REGIONAL
MODELS SHOW THE CYCLONE SLOWING BETWEEN 24 AND 48 HOURS IN RESPONSE
TO THE INFLUENCE OF AN MID- TO UPPER-LEVEL TROUGH THAT IS CURRENTLY
NORTH OF 25N AT THE SAME LONGITUDE OF THE DEPRESSION. THE TROUGH
SHOULD CUTOFF AND RETROGRADE WEST-SOUTHWESTWARD. THIS HAS THE
COMBINED EFFECT OF WEAKENING THE WEST-NORTHWESTWARD STEERING AS
WELL AS INDUCING RATHER STRONG SOUTHWESTERLY SHEAR AT THE LONGER
TIME PERIODS. THE FORECAST TRACK IS THE CONSENSUS OF THE
GFS...UKMET...GFDL...AND HWRF MODELS AND IS SLIGHTLY SOUTH OF THE
PREVIOUS OFFICIAL FORECAST. THE ECMWF AND NOGAPS MODELS ARE
DISCOUNTED AS THEY UNREALISTICALLY TAKE THE DEPRESSION NORTHWARD
ALMOST IMMEDIATELY.
THOUGH THE DEPRESSION IS OVER WARM 28C WATERS...NONE OF THE
INTENSITY GUIDANCE TAKES TD EIGHT TO A HURRICANE IN THE NEXT FIVE
DAYS. THIS MAY BE DUE TO THE CLOSE PROXIMITY TO RATHER DRY AIR
JUST TO THE NORTH AND WEST OF THE SYSTEM IN THE EARLY TIME PERIODS
AND THE RATHER SHARP INCREASE IN SHEAR AT THE LATER TIME PERIODS.
THE INTENSITY FORECAST IS CLOSE TO THE SHIPS AND LGE MODELS THROUGH
THREE DAYS AND A BLEND OF THESE TWO WITH THE GFDL AND HWRF MODELS
AT DAYS FOUR AND FIVE.
FORECAST POSITIONS AND MAX WINDS
INITIAL 13/0300Z 13.4N 46.4W 30 KT
12HR VT 13/1200Z 13.9N 47.6W 35 KT
24HR VT 14/0000Z 14.3N 48.6W 40 KT
36HR VT 14/1200Z 14.6N 49.5W 45 KT
48HR VT 15/0000Z 15.0N 50.6W 50 KT
72HR VT 16/0000Z 16.0N 53.5W 55 KT
96HR VT 17/0000Z 17.0N 56.5W 50 KT
120HR VT 18/0000Z 18.0N 59.0W 45 KT
$$
FORECASTER LANDSEA/PASCH
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